The present invention refers to a shutter for regulating the fluid flow in an absorber pipe of a solar-thermal power plant, in particular a power plant with a plurality of absorber pipes.
In a solar-thermal power plant, the energy source is solar radiation concentrated by optical installations such as heliostats or parabolic grooves. In contrast to the energy sources of conventional steam generators, solar radiation cannot be controlled, but is susceptible to a continuous change due to the diurnal and seasonal course of the sun. Here, the intensity of the impinging radiation, as well as the distribution of the radiation on the absorber change.
In a receiver, comprising, e.g., a plurality of absorber pipes with volumetric absorbers installed therein, the concentrated solar radiation is absorbed and transferred to a heat transfer medium, e.g., a fluid such as air. For technical exploitation of the energy in the heat transfer medium, it is required, in particular with volumetric receivers that the outlet temperature of the fluid should be as constant as possible across the cross-section of the receiver. To this end, the mass flow distribution of the heat transfer medium has to be adjusted over the receiver surface so as to correspond to the distribution of the intensity of the impinging radiation.
Typically, the mass flow distribution of the fluid is realized in the receiver by means of fixed shutters. Due to the high temperatures that can exceed 1000.degree. C., and also for cost reasons, these shutters cannot be controlled actively, which results in the fact that a homogenous outlet temperature can generally be reached for a single optimum operation point, only. The optimum operation point of the mass flow distribution is usually selected such that an energetic maximum, averaged over a year, is reached with respect to the optimum operation. Thus, the optimum operation is based on an average radiation distribution. Deviations of the real distribution of the impinging radiation, as occur in operation, from the average distribution can easily cause local overheating of receiver parts. In practice, the impinging radiation on the receiver is reduced in such cases, resulting in the plant not being able to use the maximum of the available concentrated solar radiation.
German Patent 44 18 951 discloses a solar energy plant with an absorber structure flown through by air, the structure being connected to a heat consuming device through a flow channel. A temperature sensor disposed on the flow channel is connected to a temperature controller controlling a fan and a throttle valve. The fan and the throttle valve connected in series therewith, adjust the air flow to the changed conditions of impinging radiation. The fan is used to regulate higher air flows, while the throttle valve is used to regulate lower air flows that cannot be adjusted by means of the variable fan. This controller is complicated and uses up a part of the energy produced by the solar energy plant, thus reducing its efficiency.